Fix unused warning in a specific feature config (#8271)

Author: andyleiserson

naga/src/back/msl/mod.rs

@@ -119,9 +119,8 @@ pub struct BindTarget {
     pub mutable: bool,
 }
 
-#[cfg(any(feature = "serialize", feature = "deserialize"))]
-#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
-#[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
+#[cfg(feature = "deserialize")]
+#[derive(serde::Deserialize)]
 struct BindingMapSerialization {
     resource_binding: crate::ResourceBinding,
     bind_target: BindTarget,